1. Field of the Invention
The present invention relates, in general, to integrated circuit (IC) packaging structures and, more particularly, to an embedded IC packaging structure which allows a micro-electro-mechanical system (MEMS) having a great number of electrodes to be bonded to another semiconductor device, such as a driver IC, using a secondary substrate, thus ensuring an easy bonding process, providing IC devices capable of executing high-speed signal processing, reducing the production costs, and improving the production yield of the IC devices.
2. Description of the Related Art
In the related art, the technical term “bonding” means an electrical connection or a physical connection between elements of semiconductor devices, such as a physical attachment of a chip to a paddle of a lead frame, an electrical wire connection of chip bond pads to inner leads of a lead frame, and a direct mounting of balls of chip bond pads to designated points of a circuit board. Conventional bonding techniques include wire bonding, TAB bonding, flip-chip binding, etc.
Wire bonding means connecting the bond pads of a monolithic chip to the inner leads of a lead frame using Au-wires or Al-wires after die bonding. In a conventional Au-wire bonding, a small diameter Au-wire unwound from an Au-wire spool passes through a capillary tube of tungsten carbide to form an Au-ball at an end of the Au-wire. The Au-ball of the wire is placed on a designated chip bond pad, and thereafter, the capillary tube is pressed downwards to bond the Au-ball to the designated chip bond pad.
In the above case, the chip has been preheated to about 360° C. which is almost equal to the eutectic point of Au—Si, the Au-wire is bonded to the designated chip bond pad by both pressure applied from the capillary tube and heat of the chip while the spherical shape of the Au-ball is deformed into a nail head shape. Such a bonding technique using heat and pressure is called “thermo-compression bonding” in the related art. After the Au-wire is bonded to the designated chip bond pad, the capillary tube is raised upwards, and then, the nail head shape of the Au-ball is deformed into a spherical shape using hydrogen gas flame. Thus, the above-mentioned Au-wire bonding is also called “ball bonding” or “nail head bonding” due to the shape of the bonded end of the Au-wire.
Another example of a conventional wire bonding technique is wedge bonding in which an ultrasonic system coupled to a wedge-shaped capillary tube of tungsten carbide is used. During a conventional wedge bonding process, an end of an Al-wire is placed on a designated chip bond pad, and then, the ultrasonic system causes ultrasonic vibration at the end of the Al-wire while the capillary tube is pressed downwards to compress the end of the Al-wire. Thus, heat is generated due to ultrasonic vibration and thermally bonds the end of the Al-wire to the chip bond pad.
After the end of the Al-wire is bonded to the designated chip bond pad, the wedge-shaped capillary tube moves to a lead frame so as to bond a designated point of the Al-wire to a designated inner lead of the lead frame in the same manner as that described for the bonding to the chip bond pad. After the designated point of the Al-wire is bonded to the lead frame, the Al-wire is cut at an appropriate position to end the wedge bonding process. In wedge bonding, Al-wires are more preferably used than Au-wires because of the material of the chip bond pads, which is Al. As the Al-wires are bonded to the Al-chip bond pads, undesired metal separation does not occur at the bonded junctions of the wires and the chip bond pads. Wedge bonding using the ultrasonic system is also called “ultrasonic bonding” in the related art.
TAB bonding means a bonding technique in which chips having metal balls on their bond pads are precisely arranged on designated positions on a polyimide tape comprising metal lead patterns formed on a polyimide film. After arranging the chips on the polyimide tape, the metal balls of the chips are bonded to the metal lead patterns of the polyimide tape.
After the metal balls of the chips are bonded to the metal lead patterns, a packaging process is executed to package the predetermined regions including the chips and bonded parts of the polyimide tape. After the packaging process, the polyimide tape is cut into pieces to provide semiconductor packages which are then mounted to a PCB (printed circuit board). In the above case, the outer leads of the packages having the polyimide tape are bonded to conductive lines of the PCB.
The polyimide tape used in the TAB bonding has perforations along opposite edges thereof in the same manner as conventional reel films for movies or conventional cassette films for photographs, so that the polyimide tape can be drawn to a desired position during a bonding process. The polyimide tape further has trimming slots with which the tape can be cut into pieces that may be stacked on top of one another during a quality test of the tape or with which the tape can be trimmed to remove unnecessary parts from the tape.
The polyimide tape has rectangular paddles on its inner area to support the chips thereon, with inner lead regions formed by dark portions defined around the paddles. Fine inner leads are arranged close together on each of the inner lead regions. The polyimide tape also has outer lead regions having outer leads which are bonded to the conductive lines of a PCB when the packages are bonded to the PCB. The process of trimming the polyimide tape and removing unnecessary parts outside the outer lead regions provides the packages to be surface-mounted on a PCB.
During a package surface-mounting process, the outer leads of the packages are bonded to the PCB. The polyimide tape further has a bonding array display pattern and a measuring pad to be used for electrical measurement of the tape.
Unlike wire bonding, TAB bonding reduces the volume and weight of packages, greatly increases the possible number of output terminals of the packages, ensures high-speed signal processing of the packages, and increases the process rate during a package production process.
During a conventional bonding process, temperature, pressure and time are recognized as important process variables. A conventional batch bonding technique in which the chip bond pads are grouped for bonding during the same system run may fail to provide constant bonding process results due to a difference in the height of the chip bond pads or due to unevenness of bonding systems, such as capillary tubes. Thus, in recent years, an individual bonding technique in which the chip bond pads are individually bonded is more preferably used.
Flip-chip bonding means a bonding technique in which a metal ball is formed on each of the chip bond pads to be directly bonded to a PCB. The flip-chip bonding technique does not need any wire bonding process, but ensures the recent trend of lightness, thinness, compactness and small size of packages, and furthermore, enhances the degree of integration and operational performance of the packages, unlike other conventional bonding techniques.
The flip-chip bonding technique removes the wire bonding process while allowing the metal bond balls to be evenly arrayed on a designated region of a chip, thus reducing the length of signal paths of circuits and thereby enhancing the frequency characteristics of the circuits. Thus, flip-chip bonding particularly improves the operational performance of a circuit having high frequency characteristics.
Of course, flip-chip bonding must be executed with chips turned upside down during a bonding process, so that the flip-chip bonding may be inconvenient during a bonding process. However, the flip-chip bonding desirably allows a plurality of different kinds of chips to be directly mounted to the same PCB, thus improving the degree of integration and operational performance of semiconductor devices and ensuring the recent trend of lightness, thinness, compactness and small size of semiconductor devices.
In the meantime, the micro-electro-mechanical systems (MEMS), which are well-known silicon semiconductor devices, have been preferably used to fabricate a variety of optical devices, such as tensiometers, accelerometers, electronic level gauges and display devices. The MEMS have ultra-fine actuators, so that the MEMS are greatly sensitive to environmental conditions. In an effort to allow the MEMS to effectively operate without being affected by the environmental conditions, the MEMS have been typically sealed in cavities of sealed packages.
U.S. Pat. No. 6,303,986 discloses “Method and apparatus for sealing a hermetic lid to a semiconductor die”. In the US patent, the semiconductor device or the MEMS is a diffraction grating light valve (GLV). An example of conventional GLVs may be referred to U.S. Pat. No. 5,311,360 disclosing “Method and apparatus for modulating a light beam”.
FIG. 1 is a sectional view illustrating a conventional semiconductor device in which a lid is hermetically sealed.
As shown in FIG. 1, a conductive ribbon 100 having a metallic conductive/reflective covering 102 is formed over an upper surface of a semiconductor substrate 104, with an air gap 106 defined between the ribbon 100 and the substrate 104. A conductive electrode 108 is formed on the upper surface of the substrate 104 and covered with an insulation layer 110.
The conductive electrode 108 is placed under the ribbon 100 at a position under the air gap 106. The conductive/reflective covering 102 extends beyond the region of the mechanically active ribbon 100 and is configured as a bond pad 112 at its distal end. The semiconductor device is also passivated with a conventional overlying insulating passivation layer 114 which does not cover the bond pads 112 or the ribbon structure 100 and 102. Control and power signals are coupled to the semiconductor device using conventional wire bonding structures 116.
The bond pads 112 are removed from the ribbon structure 100 and 102 to provide a lid sealing region 118. A solderable material 120 is formed onto the lid sealing regions 118 using a conventional semiconductor processing technique. Furthermore, a hermetic lid 122 is joined to the semiconductor device. In the above case, the lid 122 is formed to a size appropriate to fit concurrently over the lid sealing regions 118, with a solderable material 124 formed in a ring surrounding the periphery of one surface of the lid 122. A solder 126 is deposited onto the solderable material 124 so that the lid 122 is joined to the semiconductor device.
In the conventional techniques, the conductive electrodes of a semiconductor device must be electrically connected through a wire bonding process to another semiconductor device which may be a driver IC of a light modulator. However, the electrical connection of the conductive electrodes to the drive IC through the wire bonding process is problematic in that the electrical connection must consume excessive time because the light modulator has a great number of conductive electrodes 201a through 201n as shown in FIG. 2.
The electrical connection of the conductive electrodes of a semiconductor device to a driver IC through the conventional wire bonding process is also problematic in that the electrical connection using the wire bonding reduces the production yield because the closely arranged conductive electrodes 201a through 201n must be carefully wire-bonded to the electrodes of the driver IC as shown in FIG. 2.
The electrical connection of the conductive electrodes of the semiconductor device to the driver IC through the conventional wire bonding process is further problematic in that the electrical connection using wire bonding increases the production costs because the conductive electrodes 201a through 201n must be individually wire-bonded to the electrodes of the drive IC as shown in FIG. 2.
Another problem experienced in the conventional techniques is that the signal processing speed of semiconductor devices is reduced due to inductor components of bond wires when the semiconductor devices are used as high-speed signal processing devices.
In the meantime, the conventional light modulators have been fabricated through TAB bonding processes in which chips having metal balls on bond pads are precisely arranged on designated positions on a polyimide tape having metal lead patterns on a polyimide film. After arranging the chips on the polyimide tape, the metal balls of the chips are bonded to the metal lead patterns of the polyimide tape.
However, the application of the TAB bonding to light modulators undesirably results in high space consumption by the light modulators, thus increasing the production costs of light modulators. Furthermore, the application of the TAB bonding to light modulators undesirably increases the bonding resistance as well as causing the quantity of allowable current to be reduced.
U.S. Pat. No. 6,452,260 discloses “electrical interface to integrated circuit device having high density I/O count” and U.S. Pat. No. 6,096,576 discloses “Method of producing electrical interface to integrated circuit device having high density I/O count”. The two US patents proposed applications of flip-chip bonding during IC device production processes in an effort to overcome the problems caused by conventional wire bonding. However, in the above US patents, cables are used to couple integrated circuits (ICs) to an outside control circuit so that the execution of flip-chip bonding is very difficult. Furthermore, due to the cables coupled to the ICs, maintenance or repair of the IC devices is not easy.
In addition, the ICs in each of the above-mentioned IC devices are placed in air so that the heat dissipating function of the IC devices is formed only by the convection of air, resulting in inferior heat dissipation from the IC devices. Furthermore, to couple the ICs to the outside control circuit using the cables, the surface areas of the ICs must be enlarged to increase the production costs of the IC devices. Another problem of the above-mentioned IC devices is that the size of the bond pads must be excessively enlarged to provide substrate support structures.